How do I use it?

How are IRs made?

Hardware is stimulated by known signal covering all audible frequencies. This known function is being convolved with hardware's function within the hardware and this signal is being recorded. Recording is then deconvolved that way so what's left is the hardware's function that can be further convolved with any signal.

To make IRs you need:

Necessary hardware - audio interface, microphone or cables depending on what you want to capture

Test tone, this can be generated in Voxengo Deconvolver and Cockos Reaverb

Guitar Cabinet IRs

It's possible to use different impulses at the same time and blend their tones. It's like using more than one microphone to record a real cabinet. It gives great results, as it's far better to change microphone type and placement rather than trying to fix everything with EQs and reverbs.

Below is an illustration of a guitar speaker with popular microphone placing spots. The closer a microphone is placed to speaker center, the more treble the tone is. There's a lot that could be written in this paragraph, but it's also great to try it out for yourself.